BRUEL & KJAER 2204 - Frequency Response of 4-Pole Networks; Tape Recording of Sound and Vibration Data

Frequency Response of 4-pole Networks.
The frequency characteristics of audio-frequency filter networks are easily
determined using the Sound Level Meter in conjunction with a B & K Beat
Frequency Oscillator e.g. Type 1022 and the Level Recorder Type 2305. See
the set-up in Fig. 9.2. An example of the output from the Level Recorder is
shown in Fig. 9.3.
oo o oooooooooooooooooooooooooooooooooo o oocoooooooooo
OP 1140
10 100
1k 10k 100k
16 3728
Fig. 9.3. Output from the Level Recorder.
Tape Recording of Sound and Vibration Data.
Sound and vibration data often yield maximum information when stored on
a tape recording . By forming the tape into a loop, transient phenomena, such
as sound from a passing vehicle, reverberation after a gun-shot etc., can be
played back continuously and analysed with B & K frequency or spectrum
analyzers.
Tl ie 2203 is ideally suited for feeding a tape recorder, for example a battery
operated model. The Sound Level Meter OUTPUT socket should be connected
to a tape recorder having an input impedance of at least 10 kohm. With a
10 kohm load the maximum peak output voltage is 10 V, and full scale
deflection on the meter corresponds to about 3 V RMS regardless of knob
setting. 1 V RMS output is indicated by roughly 1/3 scale deflection, i.e. about
0 dB on the main scale, and since many instrumentation tape recorders require
a nominal recording level of 1 V RMS, the Sound Level Meter is an excellent
recording-level monitor. More than this, it is an ideal "calibrated source"
because whatever the input signal the output from the Sound Level Meter
is
within a suitable, known range.
Even in the case of a recorder requiring 3 V RMS input there is little chance
of peak limiting, because 10 V is acceptable and this allows a peak RMS ratio
of more than 3.
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